DELAWARE - Pat Tiberi ignited a free-for-all last fall when he said he would resign his seat in Congress.

The 12th District, shaped like an elongated letter C, runs from Mansfield to the northern Columbus suburbs, then stretches eastward to Zanesville and southern Muskingum County. The district long has been represented by a certain kind of Republican. Before he became governor, John Kasich won the seat in 1982, then passed it in 2001 to Tiberi, who had worked in Kasich's office.

Tiberi's retirement to run a lobbying group of Ohio CEOs leaves an opening to rebrand the district. Will it continue to be represented by moderate, establishment Republicans, or will it trend toward grassroots conservatives? Will Democrats find a candidate who can galvanize moderate Republicans and Trump opponents and try to turn the district blue for the first time since the early 1980s?

Anything could happen, experts say. Cook Political Report, a leading source of analysis on congressional races, on Friday labeled the district a "toss-up." The race is likely to attract national attention and spending as Democrats seek to take control of Congress.

Eighteen Republicans and Democrats are vying for the seat. Most are running both to finish Tiberi's term this year and to win the seat for the 2019-2020 term. The primary for both races is May 8. The top Republican and the top Democrat will face off Aug. 7 for the rest of Tiberi's term and Nov. 6 for the 2019-2020 term.

Here's a rundown of the main players in the race:

The establishment GOP favorite

State Sen. Troy Balderson, R-Zanesville, is the most likely to carry the mantle of Tiberi and Kasich in this seat. He has won the endorsement of Tiberi. In his time as state senator, he sometimes served as an ally to Kasich.

Balderson has also attracted donors who believe a more mainstream Republican is needed to defeat Democrats in this toss-up race. They worry a more conservative candidate could alienate moderates.

At a debate in Delaware this month, Balderson echoed one of Kasich's mantras about the importance of being business-friendly. (For these Republicans, that means low taxes, balanced budgets and the like – with the goal of creating jobs.)

"It brings people up when they’re working," Balderson said. "Democrats and Republicans can agree on the No. 1 thing of creating jobs."

The grassroots conservative darling

Melanie Leneghan(Photo: Provided)

Melanie Leneghan, a trustee in Liberty Township north of Columbus, has the backing of U.S. Rep. Jim Jordan, R-Urbana, who founded the ultra-conservative Freedom Caucus. "I am a constitutional conservative, I am a Christian conservative, and I am a Trump conservative," she said at the Delaware debate.

For instance, she says: The Environmental Protection Agency was unconstitutional and the Department of Education should be one-tenth its current size.

"Our government is way out of control," she said at the Delaware debate. "If you think 'the swamp' having more power than you is a good thing, then you wouldn’t like me very much."

What's in a name? (Republican edition)

Carol Hamilton O'Brien.(Photo: Submitted)

Other Republicans could use their name recognition to make a run. In a crowded primary like this one, the winner often gets less than 50 percent of the vote, making it easier for a surprise candidate to rise to the top.

For instance, Carol O'Brien is the prosecutor for Delaware County, a population center for Republicans, and has the backing of that county's Republican Party. Kevin Bacon (no, not the movie star) is another state senator from Franklin County and is similarly backed by his county party. On the right day, with the right voters turning out, either of them could make a run for the nomination.

State Sen. Kevin Bacon(Photo: Enquirer file)

There's even a John Adams in this race. (No, not the founding father – this one is an Air Force veteran who owns an industrial chemical company.)

The establishment Democrats' favorite

Danny O'Connor is an attorney who was elected Franklin County recorder in 2016. He's hoping the backing of the Franklin County Democratic Party will boost him to the nomination.

"You haven't had real representation in this seat for a few decades," O'Connor said at the Delaware debate, in a dig at Kasich and Tiberi.

Danny O'Connor(Photo: Provided)

He's making a case for electability, hoping to galvanize Democrats to take back the seat in Congress. That means promising to preserve veterans' benefits and entitlements such as Social Security and Medicare; pushing for a ban on assault weapons and expansion of gun background checks; and opposing Trump. Instead of a border wall, "I want to spend our money right here in the 12th district," O'Connor said.

The grassroots activists' favorite

For much of 2017, anti-Trump activists with the group Indivisible hounded Tiberi, pressing him to hold open town-hall meetings and defend the Affordable Care Act. Galena's John Russell, a Cornell University-educated farmer, was a leader in that movement.

John Russell(Photo: Photo provided)

Russell hopes to leverage that activism and his experience as a farmer in connecting with voters.

"Like any self-respecting farmer, I own guns. But we also have a right to stay safe and alive and free from fear in places like schools," Russell said at the Delaware debate. "Millions of other reasonable gun owners like me believe in stronger laws that can save lives."

He supports background checks on all sales at gun shows, laws that allow judges to take guns from people who are threatening violence, and regulations of assault weapons "that target firepower, not the style of weapon."

Zach Scott(Photo: Provided)

What's in a name? (Democratic edition)

Franklin County Democrats will recognize the name of Zach Scott, their former sheriff, who could use a law enforcement background to appeal to moderate Republicans.

But Scott is coming off two bitter losses – the Columbus mayor race in 2015 and then his re-election bid as sheriff in 2016. To say he is at odds with the Franklin County party is an understatement.

Jackie Patton(Photo: Provided)

More women are running for Congress in 2018 than ever before, most of them Democrats, according to figures analyzed by the Associated Press. Yet only one Democratic candidate in the 12th District is a woman.

Jackie Patton, a school nurse-turned-Columbus City Schools administrator, could get the vote of people who want to send women to Congress to oppose President Donald Trump and Republicans in Congress.